1. Field of the Invention
The present invention relates to a semiconductor component, and is more particularly concerned with a power thyristor.
2. Description of the Prior Art
A semiconductor component of the general type with which the present invention is concerned is disclosed in the British patent application No. 24,028. A semiconductor body has at least two zones of alternately opposed conductivity type, whose anode is connected over the entire surface to an anode electrode and has recombination centers in the semiconductor body. At least one layer, which serves to getter the recombination centers is arranged on the cathode. A drop in the concentration of the recombination centers occurs from the anode and cathode side toward a central zone which is divided, at least on the anode side, into zone elements which exhibit different concentrations of recombination centers. The ratio of the zone elements is set to be such that in the central zone, the anode-side mean value of the concentration of the recombination centers is higher than the cathode-side mean value of the concentration of the recombination centers.
A semiconductor component of this type can, for example, consist of a thyristor or a diode. The semiconductor body of a thyristor generally possesses four zones of alternately opposite conductivity type, with a pn junction arranged therebetween. The pn junction between the outer and inner anode-side zone is the blocking pn junction across which the major part of the blocking voltage drops. The semiconductor body of a power diode fundamentally possesses two zones of opposite conductivity type. The semiconductor bodies of such semiconductor components have a specific content of recombination centers which serve to influence basic electrical properties, for example the turn-off time of the component. The aforementioned recombination centers are generally heavy metal atoms, such as gold, platinum, or manganese.
The processes employed in the production of the abovementioned semiconductor components entail the gettering of a specific part of the introduced recombination centers in layers close to the surface. These are, for example, in particular layers highly doped by boron or phosphorus, or layers close to the surface whose crystal construction is considerably disturbed by mechanical processing. As a result of the gettering, there is a reduction in the concentration of the recombination centers in the semiconductor body beneath the getter layers. If uniformly gettering layers are arranged at the anode side and the cathode side, the concentration of the recombination centers exhibits a U-shaped, symmetrical profile over the thickness of the semiconductor body. If, on the other hand, as a result of a lesser disturbance of the surface, a weaker gettering effect prevails at the anode side than at the cathode side, at the anode side the concentration of the recombination centers is higher than at the cathode side and the aforementioned profile becomes asymmetrical.
For many applications it is desirable to deliberately set an asymmetry so that a determinate gradient of the concentration of the recombination centers forms in the central zone. "Central zone" is to be understood to be that zone within the semiconductor body which lies between the two flanks of the U-shaped profile, i.e. between the steeply ascending gradients of the concentration. The absolute degree of the concentration of the recombination centers can be set by the quantity of recombination centers which is diffused into the semiconductor material. However, it is not possible to influence the symmetry of the profile of the concentration of recombination centers so as to be reproducible either by controlling the quantity of recombination centers or by controlling the diffusion parameters during the diffusion process.
The concentration of recombination centers at the blocking pn junction of a thyristor and at the pn junction of a diode fundamentally determines, for example, the reverse current characteristics of a semiconductor component of this type. By virtue of the selection of the gradient of the concentration of the recombination centers in the central zone it is possible to produce semiconductor components which, with a predetermined forward voltage drop, have either a shorter turn-off time or a more favorable reverse current characteristic, and to produce components which have a symmetrical profile of the concentration of recombination centers.
In the aforementioned British patent application, it has been proposed that the gradient of the concentration of the recombination centers be set in that the anode-side region of the central zone be divided into zone elements having differing concentrations of recombination centers, and that the ratio of the zone elements be set to be such that in the central zone the anode-side mean value of the concentration of recombination centers is higher than the cathode-side mean value.
It has now been established that with an arrangement of this type, relatively high blocking currents could be noted, in particular when the entire anode-side was divided into the aforementioned zone elements.